Adherence rates of patients to a self-administration protocol for therapeutics and diagnostics over an extended or indefinite duration is often poor, with adherence rates for oral therapies for chronic asymptomatic conditions estimated to be less than 50%. The challenge of low adherence rates is greatest in primary and secondary prevention applications where a disease to be prevented or treated is often asymptomatic and the therapy has no immediate tangible benefit. Many factors contribute to low adherence rates including treatment cost, access, side effects, and the inconvenience of dosing regimens.
Current state-of-the-art approaches to improving adherence rates include educational interventions, telephone-based counseling, health information technology solutions, interactive pharmacy tools, and changing models of payment for care, such as no-copayment plans after myocardial infarction. All of these approaches have achieved only modest improvements. Meanwhile, pharmacologic solutions to the adherence rate problem generally involve invasive delivery structures and a subset of pharmacologic agents formulated for extended release. Recent advances in extended release pharmacologic systems are predominantly limited to subcutaneous, transdermal, intravaginal, surgical implants and intramuscular injections. Conventional solutions include invasive modalities such as surgical implants (including, e.g., wireless, programmable structures available from MicroCHIPS, Inc. (Lexington, Mass.)) or modalities limited to specialized applications such as birth control (including, e.g., NuvaRing® and Implanon®, both available from Merck & Co., Inc. (Whitehouse Station, N.J.)). Structures like those available from MicroCHIPS are also limited to delivering therapeutic agents with high potency because they can be administered in only microgram or smaller quantities.
Oral administration has the potential for the widest patient acceptance; however, no oral delivery system has been demonstrated to enable extended release beyond 24 hours via the oral route due to a number of fundamental barriers. Principally, the transit time for a bolus of food through, for example, the human gastrointestinal tract is rapid, typically lasting about 24 to 48 hours and including about 1 to 2 hours in the stomach, about 3 hours in the small intestine, and about 6 to 12 hours in the large intestine. One strategy for extended duration therapeutic delivery, therefore, would be to prolong the transit time of an orally-administered therapeutic (but not food). Gastric residence and/or slowed transit could be attempted and/or tolerated at a number of segments of a gastrointestinal tract, as evidenced by bezoars and bariatric structures. Bezoars (i.e., masses found trapped in the gastrointestinal system) can form from a variety of materials that are indigestible (such as food aggregates and hair) and often become clinically apparent in adult humans only at sizes in the hundreds of grams. A bariatric structure, such as an endoscopically-administered intra-gastric balloon, can be used to fill a portion of a patient's stomach to achieve noninvasive gastric reduction for weight loss. Previous attempts at gastric residence for drug delivery include mucoadhesion, gastric swelling, and flotation on gastric fluids. However, none of these approaches have even demonstrated gastric residence for more than 24 hours, let alone progressed to clinical use.